1. Field of the Invention
The present invention relates to a magnetic head and more particularly to a magnetic head which performs magnetic recording or reproduction of information to or from a magnetic disc used as a magnetic recording medium.
2. Description of the Prior Art
Referring to FIGS. 1 to 3, an explanation is provided of a magnetic head which performs magnetic recording or reproduction of information to or from a flexible magnetic disc, a floppy disc, by the so-called tunnel elimination method as an example of the above-described type magnetic head.
FIG. 1 illustrates the construction of a body of such a magnetic head. In FIG. 1, reference numeral 1 denotes a front core assembly hereinafter, abbreviated as a "core assembly"). The core assembly 1 is constructed as a combination of a magnetic core for recording and reproduction (hereafter, referred to as a "recording/reproduction core") and an elimination magnetic core 4 for performing tunnel elimination hereinafter, referred to as an "elimination core") with their respective front core portions being connected to each other via a spacer 6.
The recording/reproduction core 2 includes a T-shaped front core 2a and an I-shaped front core 2b connected to each other via a recording/reproduction gap 3, with each of the back ends of the front cores 2a and 2b being connected to a back core 15. The elimination core 4 includes a T-shaped front core 4a and an I-shaped front core 4b connected to each other via elimination gaps 5a and 5b, with each of the back ends of the front cores 4a and 4b being connected to a back core 16. In this case, the recording/reproduction core 2 and the elimination core 4 are connected to each other via the spacer 6 to form the core assembly 1 before the cores 2 and 4 are connected to their respective back cores 15 and 16, and sliders 7 and 8 are connected on both sides of the assembly core 1 by, for example, gluing, glass welding or the like.
The sliders 7 and 8 are made of ceramics or the like, and slidably contact a magnetic disc (not shown) together with both cores 2 and 4 to stabilize the slidable contact of both cores 2 and 4 onto the magnetic disc, thereby protecting the cores 2 and 4 from damage. The sliders 7 and 8 are blocks each having an L-shaped cross section and being formed with recesses 7b and 8b, on lower portions of their respective side surfaces opposite to the core assembly 1. The sliders 7 and 8 are connected to the core assembly 1 on their respective facing surfaces 7a and 8a, i.e., upper portions of their respective side surfaces opposite to the core assembly 1.
After the connection, a coil bobbin 9 on which a coil 10 for recording or reproduction is wound around and a coil bobbin 12 on which a coil 13 for elimination is wound around are fitted to the core assembly 1 so that the front cores 2a and 4a are inserted into respective cavities of the coil bobbins 9 and 12. Thereafter, the back cores 15, 16 connected to each other via a spacer 17 are connected to the back ends of the front cores 2a, 2b, 4a and 4b to construct the magnetic head body 18 shown in FIG. 2. As shown in FIG. 2, the magnetic head body 18 is fixed to a support plate 19 of stainless steel or a beryllium-copper alloy, which in turn is fixed to a flexible printed board 20, and coil ends 10a and 13a are connected to the flexible printed board 20, thus constructing a magnetic head 21.
The magnetic head 21 thus constructed is attached to a disc drive unit (not shown) by fixing the support plate 19 to a head carriage of the unit and is slidably contacted on the magnetic disc, with the upper surfaces of the core assembly 1, and of the sliders 7 and 8 (FIGS. 1 and 2) serving as a slidable contact surface. Recording is performed by the tunnel elimination type system shown in FIG. 2.
That is, in the tunnel elimination system, a data track 22 is formed by recording data to the magnetic disc slidably moving in a direction indicated by the arrow shown in FIG. 3 using the recording/regeneration gap 3 and then eliminating both sides of the data using the elimination gaps 5a and 5b, respectively.
Recently, however, development of higher capacity floppy disc units has been promoted and units which have a capacity of 10 MB or more have already been fabricated and put on the market. A higher capacity floppy disc unit can be attained by increasing the linear recording density and track density thereof. Floppy disc units having a capacity of from 1 to 2 MB now available on the market have a maximum linear recording density of 9.7 KBPI and a track density of 135 TPI. However, in order to obtain a capacity of 10 MB or more, it is necessary that the floppy disc units have a maximum linear recording density of 35 KBPI or more and a track density of 405 TPI or more. In other words, they must have both maximum linear recording density and track density by from 3 to 4 times as high as those now available.
In the case where the track density is to be increased, a servo signal type recording in which a servo signal has already been recorded in the magnetic disc is used in place of the tunnel elimination type recording using the magnetic head 21 as shown in FIGS. 1 and 2. FIG. 4 illustrates a situation in which recording to a magnetic disc is performed according to the servo signal type recording. In this case, the positioning of tracks is performed by a servo signal 24 which has been already recorded in the magnetic disc, and data are recorded using a magnetic head with only the recording/reproduction core 2 having only the recording/reproduction gap 3, thus forming a data track 22.
The above-described servo signal type recording is used for floppy disc units having a high track density as high as 200 TPI or more.
On the other hand, in general usage of floppy disc units, compatability must be assured between upper grade model units and lower grade model units so that their software and data are kept compatible. For example, 3.5 inch type products having a capacity of 2 MB have a 1 MB R/W compatibility (that is, they can read from or write to 1 MB floppy discs), and products having a capacity of 4 MB have a 1 MB and 2 MB R/W compatibility (that is, they can read from or write to both 1 MB floppy discs and 2 MB floppy discs). However, it is because the floppy discs have the same track density of 135 TPI that R/W compatibility is obtained. If the track density is different one from another, it is possible to read out from those floppy discs with lower track densities but not to write to them, thus failing to assure compatibility of data between floppy discs with different track densities.
Accordingly, in order to keep compatibility between floppy discs with different track densities, a composite type magnetic head has been proposed in which a tunnel elimination type magnetic core and a servo signal type magnetic core are arranged parallel or side by side in the direction of track width. FIGS. 5, 6, 7A and 7B illustrate the construction of such composite type magnetic head. In FIGS. 5, 6, 7A and 7B, those parts which are common with or correspond to those illustrated in FIGS. 1 and 2 are indicated by the same reference numerals, and explanation of the common parts is thus omitted here.
FIG. 5 is an exploded perspective view of the magnetic head body.
In FIG. 5, the tunnel elimination type recording/reproduction core 2 and elimination core 4 are constructed by the core assembly 1 and the back cores substantially the same as those illustrated in FIGS. 1 and 2. Both cores 2 and 4 are constructed for a track density of 135 TPI, for example. Differences from those illustrated in FIGS. 1 and 2 are that the coil bobbin 12 of the elimination core 4 is engaged with the back core 16 in order to avoid a coil bobbin 27 for a recording/reproduction core 40 on which explanation will be made hereinbelow. To achieve this, the back core 16 is formed to be long and the front core 4a is substantially L-shaped.
On the other hand, reference numeral 40 denotes a servo signal type recording/reproduction core, which is constructed so as to be useful for floppy disks having a high track density (for example, 405 TPI or 540 TPI). The recording/reproduction core 40 has a back core 29 connected to a lower end portion of a core assembly 25 as illustrated in FIG. 5. The core assembly 25 includes an L-shaped front core 25a and a T-shaped front core 25b connected to the L-shaped front core 25a via a recording/reproduction gap 26. The front core 25b is inserted into the bobbin 27 around which a coil 28 is wound.
In assembling the magnetic head body, at first the core assemblies 1 and 25 are bonded to each other with an adhesive via a filler plate 30 made of non-magnetic ferrite or ceramics. The filler plate 30 has the shape of a slender rectangle in accordance with the facing surfaces on the upper ends of the respective side surfaces of the core assemblies 1 and 25.
Next, the sliders 7 and 8 are connected on both sides of the core assemblies 1 and 25. FIG. 7A illustrates the side surface in the above-described condition. FIG. 7B illustrates a frontal view of the core assemblies to which only the slider 8 is connected.
Then, after engaging the coil bobbins 9 and 27 with the respective front cores 2a and 25b, the coil bobbin 12 is engaged with the back core portion 16 in the assembly composed of the back cores 15 and 16 connected to each other via the spacer 17 and then the back cores 15 and 16 are connected to the front cores 2a and 2b, and 4a and 4b, respectively. The back core 29 is connected to both of the front cores 25a and 25b. Thus, a magnetic head body 31 is constructed.
Upon performing recording/reproduction of a magnetic disc unit (not shown) using the magnetic head body 31 having the above-described construction, R/W compatibility is possible between upper grade model disc units and lower grade model disc units by using one core appropriately selected from the cores 2, 4 and 40 even when the track density is different from one floppy disc to another.
However, in the construction of the above-described composite type magnetic head, as will be clearly understood from FIG. 7B, the filler plate 30 of a slender rectangle is connected only on the respective side surfaces of the upper ends of the core assemblies 1 and 25, and the area of connection between the core assemblies 1 and 25 and the filler plate 30 is small. Therefore, the connection strength between the core assemblies 1 and 25 and the filler plate 30 is low. As a result the magnetic head body 31 tends to be broken upon processing the slidable contact surface 32 of the magnetic head body 31 for contacting the magnetic disc, or there tends to occur a difference in height between the core assemblies 1 and 25 and the sliders 7 and 8 or the filler plate 30 upon assembling the magnetic head body. This causes problems in that the characteristics of the magnetic head are deteriorated and yield is decreased.